Corrosion resistance of decorative chromium electroplated objects

ABSTRACT

IMPROVED CORROSION RESISTANCE RESULTS IN DECORATIVE CHROMIUM PLATED OBJECTS HAVING CHROMIUM PLATED OVER NICKEL BY TREATMENT OF THE SURFACE CHROMIUM LAYER BY IMPINGEMENT OF SOLID PARTICULATE MATTER SO AS TO FORM MICROPORES IN SAID CHROMIUM LAYER. THESE MICROPORES EXTEND THROUGH SAID CHROMIUM LAYER TO THE UNDERLYING NICKEL LAYER. THE NUMBER OF MICROPORES PER SQUARE INCH SHOULD EXCEED 3,000 AND PREFERABLY BE IN THE RANGE OF 40,000200,000 PER SQUARE INCH FOR DECORATIVE CHROMIUM PLATED OBJECTS DEPENDING ON THE TYPE OF PARTICLE, SIZE OF PARTICLE, DENSITY OF PARTICLE AND MOMENTUM AT IMPINGEMENT. LIKEWISE, MULTIPLE NICKEL COATINGS CAN BE USED AND OTHER UNDERLYING METAL LAYERS SUCH AS COPPER CAN BE INTERPOSED BETWEEN THE SUBSTRATE AND THE NICKEL AND CHROMIUM SURFACE LAYERS.

United States Patent 3,625,039 CORROSION RESISTANCE OF DECORATIVECHROMIUM ELECTROPLATED OBJECTS Theo G. Kubach, Drosselweg 68,Leonberg-Silberberg,

Germany; and Werner H. R. Pritsch, Thomastrasse 57;

and Wilfried Bolay, Saumweg 29, both of Stuttgart,

Germany No Drawing. Filed Aug. 28, 1969, Ser. No. 853,977

Int. Cl. C216 7/06 US. Cl. 72-53 9 Claims ABSTRACT OF THE DISCLOSUREImproved corrosion resistance results in decorative chromium platedobjects having chromium plated over nickel by treatment of the surfacechromium layer by impingement of solid particulate matter so as to formmicropores in said chromium layer. These micropores extend through saidchromium layer to the underlying nickel layer. The number of microporesper square inch should exceed 3,000 and preferably be in the range of40,000- 200,000 per square inch for decorative chromium plated objectsdepending on the type of particle, size of particle, density of particleand momentum at impingement. Likewise, multiple nickel coatings can beused and other underlying metal layers such as copper can be interposedbetween the substrate and the nickel and chromium surface layers.

IMPROVEMENT IN THE CORROSION RESISTANCE OF DECORATIVE CHROMIUMELECTROPLAT- ED OBJECTS This invention relates to a means for improvingthe corrosion resistance of chromium electroplated objects. Moreparticularly, this invention provides for enhancing corrosion resistanceof decorative nickel-chromium electroplated articles by inducingmicroporosity in the chromium by means of impingement of solid materialson said surface chromium layer.

In the recent past, it has been discovered by various workers in thefield, that decorative chromium can be improved, with respect tocorrosion resistance by effecting the formation of micropores in thechromium layer. U.S. Pats. 3,298,802 and U .3. 3,449,223 illustrateexamples of such decorative chromium of improved corrosion resistance.In US. 3,298,802 an object which may or may not be electrodeposited withother metal coatings, receives a continuous bright nickelelectrodeposit. This bright nickel electrodeposit is followed by a thinelectrodeposit of nickel which incorporates various solid particulatematter which is non-conductive into said thin nickel layer. Thereafter,chromium is electrodeposited on said particulate containing nickellayer. The particles in the nickel layer interfere with the flow ofcurrent during electrodeposition of the chromium layer and result in theformation of a microporous chromium deposit. US. 3,449,223 discloses asimilar process which calls for a particulate containing bright nickellayer being plated directly on a substrate without the need for anunderlying particle-free bright nickel layer.

Applicant has now discovered that this same improvement in corrosionresistance can be obtained in decorative chromium plated objects byforming micropores in the chromium surface after the final chromiumlayer has been electrodeposited on said object. The micropores areformed in the chromium surface by causing particulate materials ofsufficient hardness to strike the surface of the chromium withsufficient force so as to form micropores.

Various particulate materials have been used with success in the instantprocess. These include round Ottawa sand (23-25 mesh), jagged sand(32-34 mesh), lead powder, polyethylene pellets x x A (Goodrich GeonVinyl #8814 white), magnesium filings, glass beads (Blastolite BLXN-l6General Steel Industries, St. Louis, Mo.), polystyrene pellets (.05"diameter), iron powder, nickel powder and powdered silica (320 mesh).Any solid particulate material would be useful in the practice of thepresent invention which has suflicient hardness to withstand the impactwith the chromium surface at least to the extent of marring saidchromium surface in the formation of a pore.

If small particulate matter is used in the practice of the presentinvention, such small particles must be given a higher velocity assumingequal density so that they possess sufficient force at impact to formmicropores. Such smaller particulate matter may be successfully used inthe practice of the instant invention by increasing the height fromwhich such matter is dropped for impinging said particles on saidchromium surface. Merely dropping such small particles short distancesonto a chromium surface would not result in sufiicient momentum toeffect such pore formation as required by the instant invention. It. onthe other hand, large particles possessing excess momentum wereemployed, they would result in dulling or destruction of the chromiumsurface unless the impacts were precisely controlled which would not becommercial- 4 ly feasible. Should lead of the same mass be substitutedfor sand, for instance, the velocity of the lead particle would have tobe somewhat above the velocity of the sand in order to accomplish thesame results, this being due to the fact that lead is more malleablethan silica and would absorb more of the force of the impact on thechromium surface.

Another factor which would influence the size, hardness and velocity ofthe particle is the chromium surface itself.

The size of the particles impinging upon the chromium surface so as toproduce the microporous condition as indicated previously may varywidely. However, generally the particles would be in the size range of15-400 mesh although larger or smaller particles can effect the sameresult under appropriate conditions.

In the practice of the instant invention, particulate matter is made tocontact the chromium surface of the object which has an underlyingnickel layer. The appropriate size particle utilizing the appropriateforce is thereby used for a sufficient period of time to form pores inthe chromium surface. To effect appreciable increases in corrosionresistance, the minimum number of pores formed should be at leastapproximately 3,000 per square inch, although lesser numbers of pores soformed effect some corrosion resistance improvement. The preferable poredensity is in the range of 40,000 to 200,000 per square inch. The poresize can be anything up to approximately a few microns. The only upperlimit on the pore concentration is that the pore formations should ceasebefore the chromium electroplate shows dulling to the human eye. Indetermining the microporosity of the chromium layer, use is made of theDubpernell test in which the composite electroplate is made cathodic inan acidic copper sulfate solution, preferably with a cell potential ofabout 0.2-0.3 volt. Copper is thus deposited only at the pores and noton the bulk of the surface where it is believed the chromium is coveredby an oxide film. The frequency of microporosity is determined by usinga microscope at -400 magnification.

The brightness of the finished article, that is after treatment of the.final chromium layer, depends on the number and size of the pores in thechromium layer. The limits could be determined by extensive laboratorywork. However, this would appear to be an unnecessary expenditure oftime and effort since visual observation of the chr0- mium layer duringtreatment foretells the finish one could expect on the final product. Ifthe treated chromium layer is overtreated it visibly dulls and a satinfinish thus results, whereas if it remains bright, a decorative chromiumfinish as contemplated by this invention will result. Thus, according tothe instant invention, impingement of solid particulate matter on thechromium layer should be stopped before said chromium surface showsdulling to the human eye.

It is surprising that porosity of the chromium can be elfected With aninsignificant effect on the brightness of the chromium surface as viewedwith the naked eye. By use of an intense light and a non-treated surfacefor comparison, it is possible to see a slight haze in the surface ofthe treated sample. It is even more surprising when it is noted thatsimilar but harsher treatments which are used for satinizing chromium orremoving metal, lead to much reduced corrosion protection.

One important object which must be kept in mind in the practice of theinstant invention is that the pores must extend through or almostthrough the chromium layer but may not extend entirely through thenickel layer underneath unless, of course, another layer of nickelunderlies said pore containing layer. Likewise, additional metalliclayers such as copper, nickel or the like can be interposed between thebase material and the nickel-microporous chromium outer layers tofurther improve corrosion resistance and the like.

The present invention is applicable to all standard bright nickel andchromium electroplating baths as an improvement in corrosion resistanceresults in each and every case over the equivalent untreated composite.

In determining the corrosion resistance, suitable accelerated testswhich correlate well with longer service tests on commercial articles ofmanufacture were used. These include the Copper Accelerated Salt Spray(CASS) and Corrodkote tests. Using these accelerated tests, theenhancement of the corrosion resistance by the practice of the instantinvention has been damatically shown.

It should be noted that when corrosion tests are made, two types ofcorrosive attack generally result. With conventional chromium-nickelsystems, pinhole corrosion occurs in relatively few sites in which rapidpenetration to the base layer generally occurs as shown by basis metalcorrosion. If the base metal for the electrodeposited coatings is steel,rust will become evident in the pinhole points of attack although theremaining bulk surface of the object may remain bright and show littleattack.

Where a nickel-chromium surface has been treated according to theinstant invention, few if any pinhole rust spots will develop over longperiods for normal thicknesses. However, shallow surface attack willoccur at the pores in the chromium and the test object will tend toappear dull and stained in varying degree due to corrosion of the nickelat the pores. However, this stain can be removed by simple washing.

The following examples illustrate the practice of the instant invention.

EXAMPLE I 4" x 6" fiat steel panels (3 per set) were plated with 0.4 milsemibright nickel onto which were subsequently plated 0.2 mil of brightnickel. These electroplating baths used to plate the nickel werestandard commercial baths and provided typical deposits well known tothose skilled in the art. After the panels had been plated with the twolayers of nickel, they were then chromium plated. The chromium depositwas 10 millionths of an inch thick and was deposited from a conventionalchromium electroplating bath having a Gro /H 50 ratio of 100: 1. Thepanels were then treated by pouring various solid materials ashereinafter described over the surface of the panel to provideimpingement of the solid materials on the panels at a 45 angle so as toform micropores in said chromium surface. Unless otherwise specified,250 cc. of the solid were poured as uniformly as possible over thesurface of 4 x 6" panel. One panel per set was Dubpernell tested and thepore count for the set determined. The remaining two panels werecorrosion tested 48 hours CASS, then 20 hours Corrodkote. Corrosion testresults are given below for the solid treated panels as well asuntreated control panels and numbers given under the corrosion testheadings refer to pinhole rust spots. All panels resulted in adecorative chromium finish with the surface being fully bright. Testparameters and results of such tests are as follows:

Drop Pinhole 21st spots ht., Pores per 32 hrs. 48 hrs. 20 hrs.

Test material inches Dubpernell test sq. in. CASS CASS Corrodkote 3 Finemleroprosity 79,s00-s9,400 g Rounded, Ottawa Sand 2325 mesh 10 d0104,000 1 4,000 g 1% is ...do 134,000-164,000 g g 36 do 22s,000-a7s, 0002 8 i 3 Fine mler0poroslty 40, 000-45, 000 g 10 do 104, 000-134, 000 g iJagge San 3 -34 e h 18 .do 492, 000-537, 000 36 .--..do 596, 000-640,000 g g 10 Medium porosity 3, 300-5, 000 g5 Pb Powder 8 .....do8,30011,600 g 36 .-...do 11, 600-16, 600 a g 10 Very coarse porosity 5%?5388 X /ie" X l ie, P lyethylene pellets 2.8% T104 (Goodrlcdl 18 do gGeon Vinyl #8814, white). 36 undo n 0 Z 11 200 10 Coarse porosity g 5%52%? M filin 18 do 83 538g 36 4 a 132 at: Ottawa Sand cc 10 Finemleroporoslty 45,000-75, 000 g g 2 Ottawa Salldi 250 10 d0 104,000- ,00013 Ottawa sand, 75 cc 4.... 10 415,000450000i 2 TABLE-Continued Pinholerust spots Drop ht., Pores per 32 hrs. 48 hrs. 20 hrs. Test materialinches Dubpernell test sq. in. CASS CASS Corrodkote 10 100 200 33 100200 Untreated std. Cr (Controls) Edge maeroeracking 9 100 200 2 38 100 460 200 33 100 200 EXAMPLE H EXAMPLE V 15 In another test 4" x 6" steelpanels (3 per set) were plated successively with 0.7 mil of semibrightnickel, 0.3 mil of standard bright nickel and 0.02 mil of chromium.After plating, two of the panels were treated with Ottawa sand (250 cc.)as described in Example I using a drop height of 6 inches. The sandtreatment resulted in the appropriate microporosity as shown by theDubpernell test performed on the third panel. The sand treated panels aswell as control panels (without the sand treatment) were CASS tested for46 hrs. and then Corrodkote tested for 60 hrs. with the followingresults:

CASS Corrodkote System 16 hrs. 46 hrs. 20 hrs. 40 hrs. 60 hrs.

Std. Cr Control i o o 20 D 0 60 Std. Cr Treated 0 0 0 0 0 D0 0 0 0 0 0EXAMPLE III -In another series of tests to determine the effect of thesand treatment on panels going directly into the Corrodkote test, 0.4mil of semibright nickel, 0.2 mil of standard bright nickel and 0.02 milof conventional chromium were electrodeposited consecutively. Thesepanels were then sand treated as described in Example II above and thenCorrodkote tested directly. Test results were as follows:

Commercially available automotive bumper wings, electroplatedsuccessively with 0.5 mil semi-bright nickel, 0.3 mil standard brightnickel and 20 millionths conventional chromium were sand treated bydropping Ottawa sand from approximately inches with distribution asuniform as possible over the surface with the following results:

Corrodkoto Bumper wing hrs. 40 hrs. 60 hrs Control 70 100 100 Sandtreated 5 6 5 Plastic panel (3 /2 x 3") were pretreated by conventionalmeans, given a thin coating of electroless nickel and then electroplatedsuccessively with 0.8 mil bright acid copper, 0.4 mil senribrightnickel, 0.2 mil standard bright nickel and 0.01 mil conventionalchromium. Panels were treated by dropping Ottawa sand from 12 inches,with the following results after the successive CASS, Corrodkote, CASSexposures indicated:

The corrosion spots represent pores through the chromium and nickel andgreen copper corrosion exuding to the surface.

All numbers in the foregoing examples under CASS corrosion testsindicate pinhole corrosion spots.

We claim:

1. A process of treating a bright decorative composite electroplate ofnickel and chromium on a metal or plastic substrate to increase thecorrosion protection of said substrate comprising impinging a solidparticulate material against the surface of the chromium with a forcesufficient to form micropores extending through the chromium layer butinsufficient to penetrate through the nickel layer or to adverselyaffect the brightness of the electrodeposit.

2. A process as described in claim 1 wherein said chromium deposit iscontacted with said solid particulate material until at least 3,000micropores per square inch are formed through said chromium deposit.

3. The process of claim 1 wherein the solid particulate material isimpinged on the substrate by dropping.

4. The process of claim 3 wherein the particulate material is droppedfrom a distance of between about 3 inches and 36 inches.

5. A process of forming micropores in the thin decorative chromium layerforming the top layer of a duplex nickel-chromium layer electrodepositedon a metallic substrate comprising contacting a chromium layer with asolid particulate material with a force and for a period of time thatare sufiicient to form micropores through the chromium layer butinsuflicient to penetrate through the nickel layer or to appreciablyaffect the brightness of the duplex layer.

6. The process according to claim 5 wherein the chromium layer iscontacted with said particulate material for a sufficient length of timeuntil at least about 3,000 micropores per square inch are formed in saidchromium layer.

7. The process according to claim 6 wherein the chromium layer iscontacted with said particulate material until between 40,000 and200,000 micropores are formed per square inch.

8. The process according to claim 7 wherein said solid particulatematerial is dropped on to the chromium layer 8 from a distance ofbetween about 3 in. and 36 in. above 3,298,802 1/1967 Odekerken 204-41said layer. 3,382,159 5/1968 Reed 7263 9. The process according to claim8 wherein the solid 3,410,124 11/1968 Makoto 7253 3,449,223 6/1969'Odekenken 29194 particulate material is sand.

RICHARD J. HERBST, Primary Examiner US. Cl. X.R.

References Cited UNITED STATES PATENTS 2,248,530 7/1941 Ellesworth29--DIG16 2,999,798 9/1961 Eisele et a1. "204-41 29DIG 36

